Dissolved organic matter (DOM) plays several important roles in forest ecosystem development, undergoing chemical, physical and/or biological reactions that affect ecosystem nutrient retention. Very few studies have focused on gross rates of DOM production, and we know of no study that has directly measured DOM production from root litter. Our objectives were to quantify major sources of total potentially water-soluble organic matter (DOMtps) production, with an emphasis on production from root litter, to quantify and compare total potentially soluble organic C, N, and P (DOCtps, DONtps, and DOPtps) production, and to quantify changes in their production during forest primary succession and ecosystem development at the Mt. Shasta Mudflows ecosystem chronosequence. To do so, we exhaustively extracted freshly senesced root and leaf and other aboveground litter for DOCtps, DONtps, and DOPtps by vegetation category, and we calculated DOMtps production (g m⁻² y⁻¹) at the ecosystem level using data for annual production of fine root and aboveground litter. DOM production from throughfall was calculated by measuring throughfall volume and concentration over 2 years. Results showed that DOMtps production from root litter was a very important source of DOMtps in the Mount Shasta mudflow ecosystems, in some cases comparable to production from leaf litter for DONtps and larger than production from leaf litter for DOPtps. Total DOCtps and DONtps production from all sources increased early in succession from the 77- to the 255-year-old ecosystem. However, total DOPtps production across the ecosystem chronosequence showed a unique pattern. Generally, the relative importance of root litter for total fine detrital DOCtps and DONtps production increased significantly during ecosystem development. Furthermore, DOCtps and DONtps production were predominantly driven by changes in biomass production during ecosystem development, whereas changes in litter solubility due to changes in species composition had a smaller effect. We suggest that DOMtps production from root litter may be an important source of organic matter for the accumulation of SOM during forest ecosystem development.
